Presently, various artificial fishing fields have been developed and used for raising fishery products, such as fish and shellfish. These types of fishing fields are intended for luring adult fish and shellfish to create an artificial fishing field. Realization of this type of fishing field has been accomplished by submerging cars, buses, tires, steel, or stone. Microorganisms attach to this debris and provide feeding areas for fish.
In addition, due to a recent trend towards a depletion of fishery resources, there is an increasing demand for developing an artificial fishing field aimed at raising or culturing fishery resources. This culturing type of fishing field is intended for sheltering and feeding juvenile fish and shellfish.
In the juvenile stages of development, the fish and shellfish feed off of microorganisms and seaweed. Therefore, it is imperative to provide adequate surfaces for microorganisms to attach or otherwise anchor onto the artificial fishing field.
Several attempts, based primarily on structural considerations, have been made to provide artificial fishing fields for culturing fish and shellfish.
U.S. Pat. No. 3,898,958 to Pranis, Jr. discloses an artificial fish farming apparatus in the form of a three-dimensional lattice framework to provide adequate surface areas for the anchoring, growth, and accumulation of microorganisms as a food supply for small fish. The basic structure of this lattice framework comprises the interconnection of pipes having various geometrical shapes and cross-sections for providing adequate surface area to support microorganisms. However, the major disadvantage of the Pranis, Jr. apparatus is its inability to provide sufficient surface area in a relatively complex structure, for enhancing the growth of microorganisms and the protection of small fish from predators.
U.S. Pat. No. 4,508,057 to Suzuki discloses an artificial fishing field unit comprised of concrete blocks having high resistance to strong waves and fast ocean currents that exist in shallow water zones. In addition, to prevent emission of strong alkali from the surface of the concrete block, crystal blocks of iron sulfate are embedded below the surface of the concrete before the concrete has been cured. The strong alkali contained in the concrete is neutralized with the acid from the iron sulfate. A plurality of these artificial fishing fields are arranged on the ocean floor for creating a culturing fishing field in shallow water zones. The major disadvantage of the Suzuki reef design is its awkward bulk associated with each artificial fishing field due to its concrete-based structure. Further, this type of artificial fishing field fails to provide adequate shelter for protecting small fish from their predators.